Conventionally known seat reclining devices having reclining mechanisms that is capable of adjusting an inclination angle of a seat back of a vehicle seat are disclosed, for example, in Japanese Laid-Open Patent Publications Nos. 2000-43625 and 2002-360368.
In the seat reclining device disclosed in the former document, operating cables are connected to the reclining mechanisms provided on right and left sides of the seat in order to individually lock and unlock these reclining mechanisms. Further, the operation cables are connected to a single releasing lever. Therefore, by operating the single releasing lever, it is possible to perform locking and unlocking operations of the reclining mechanisms in synchronism with each other on the right and left sides. However, the structure in which a plurality of operating cables are used has a problem because relatively high costs are involved. Further, because the individual operating cables have respectively different length, the operation cables may have different amounts of elongation when they are operated. This may result in a problem because a gap in operation timing of the two reclining mechanisms can be produced.
In the seat reclining device disclosed in the latter document, operation shafts for performing locking and unlocking operations of the right and left reclining mechanisms are connected to each other via a connection member so as to transmit rotational motion therebetween. Therefore, upon operation of one of the operation shafts, the rotational motion thereof is transmitted to the other of the operation shafts. As a result, the locking and unlocking operations of the right and left reclining mechanisms can be conducted in synchronism with each other. Transmission of an operational force via the connection member is secured by torsional rigidity of the connection member. According to this structure, as compared with the above-mentioned structure using a plurality of operating cables, relatively low costs and reduced numbers of parts are involved. In addition, it is preferred because a gap in operation timing of the two reclining mechanisms cannot be easily produced.